Digital acquisition devices, such as the Tektronix TLA7000 Logic Analyzer, enable electrical engineers to measure the signals produced by the digital systems that they design. Research labs use digital acquisition devices to observe correctness of timing and intensity of signals in microprocessors, memory, buses, and other components of digital systems. Acquisition devices play a major role in the development of the continually advancing electronics industry.
A digital acquisition device will typically display a sensed signal as a sharply elevated or descending step. The rise from “off” to “on” and the descent from “on” to “off” is usually synchronized with the period of a clock in the system under test, and the transition from one state to the other is represented visually as a vertical edge. It is useful to distinguish the clock of a system under test from a clock of a digital acquisition device. In order to provide high resolution on the signal under test, the sample clock of the digital acquisition device must pulse, and therefore sample the signal under test, at a frequency higher than the frequency of the tested system's clock. This yields meaningful measurements to engineers using the acquisition device. The distance between two consecutive pulses of the clock for the digital acquisition device may be referred to as a sampling bin, and the pulse itself is the sampling bin boundary. A rising or falling edge in an ideal scenario will consistently land within a single sample bin and, therefore. will be consistently associated with a single sample clock edge.
When testing a particular design, engineers sometimes measure a signal occurring in a repeated pattern. The acquisition device may be programmed to begin data acquisition with a trigger, which can itself be a rising or a falling edge. By supplying a repeating input, engineers can observe whether an input predictably and reliably generates a consistent output. Under ideal circumstances, the output is displayed as a static series of steps if the device is working as expected. Circumstances, however, are not always ideal.
Depending on metastable conditions (inability of the system under test to settle on a stable “on” or “off”), noise, and skew relative to the trigger event, edges often fall within a sampling bin and not directly on the sampling bin boundary. Multiple edges are drawn then on the screen of the acquisition device to represent what is actually a single edge appearing in multiple acquisitions. These edges appear to chatter on the X-axis by two or more sampling bin boundaries as the live acquisition continually updates. This leads to a confusing display of limited usefulness. The live update of digital channels would be made more meaningful if the chatter could be eliminated.
Accordingly, there remains a need for an improved method of displaying a waveform for a digital acquisition device.